1. Field of the Invention
The present invention relates to a pulse Doppler radar device for detecting a range to an object in vicinity and a relative velocity of the object at the same time. And in particular, the present invention relates to a pulse Doppler radar device making use of a pulse with an ultra wideband.
2. Description of the Related Art
Conventionally, as a pulse Doppler radar device for vehicle for detecting a range to and a relative velocity of an object, there is known a type as disclosed in a Patent Reference 1 for example. The pulse Doppler radar device for vehicle as disclosed in the Patent Reference 1 emits a pulse, and then receives a reflected wave, which is reflected by an object.
The reflected wave, which is received thereat, is sampled for each of range gates (or range bins). The sampled data is presum-processed, and then the presum-processed data is subjected to an FFT (a fast Fourier transform) processing. In the FFT processing, a frequency analysis is performed for a signal at each of the range gates, and then an amplitude output is evaluated for each of frequency gates. Further, after performing such processing, a range to an object is evaluated based on the range gate at which the signal is detected, and also a relative velocity of the object detected at the range gate is evaluated as well based on the frequency gate at which the signal is detected. Furthermore, the Patent Reference 1 proposes performing a presum-processing over a plurality of range gates in a receiving circuit in order to improve an S/N (signal to noise) ratio.
Patent Reference 1: Japanese Patent Application Publication No. 2004-125591
However, the operation mode of a radar device for vehicle includes a case where the radar device is used in a period of running at high speed, such as a collision detecting radar or the like, and a case where the radar device is used in a period of running at lower speed, such as a parking support radar or the like. And then an operating condition required, such as a range resolution, a measuring range (ranging area), a measuring cycle (data renewal cycle), or the like, is different for each case. In the former case of the collision detecting radar or the like, the range resolution may be as rough as several tens centimeters approximately, however, there is a requirement for detecting an object having a large relative velocity of up to approximately 200 km/h within a ranging area. On the other hand, in the latter case of the parking support radar or the like, the range resolution should be finer than 10 cm for example, however, it is sufficient if it is possible to detect an object having a relative velocity not larger than 20 km/h for example.
Moreover, a data renewal cycle (measuring cycle) required for notifying a result of a radar detection to a crew is different depending on the operation modes. That is, in the former operation mode of the collision detecting radar or the like, because the relative velocity to an object is large, the measuring cycle needs to be as short as approximately 10 ms for example. On the other hand, in the later operation mode of the parking support radar or the like, the measuring cycle may be about ten times as long as that in the former case because the relative velocity of the object is smaller.
Thus, it has been necessary to install separate radar devices corresponding to different operation modes. However, installing a plurality of radar devices requires an excessively large installation space, which makes it difficult to install the radar devices and makes the system costly.
The present invention is made to solve the above mentioned problems. It is an object of the present invention to provide a pulse Doppler radar device which is capable of automatically judging a change of the operation mode and switching an operating condition.